1. Field of the Invention
The present invention relates to a method for forming a microfine structure comprising a metal on a substrate, and a microfine structure forming body formed by the method.
2. Description of Related Art
Recently, photolithography techniques have been used frequently for processing a microfine pattern required for semiconductor devices, etc. However, it has become difficult to process such a microfine pattern by the photolithography techniques, as the formation of extremely small patterns has progressed, and the required pattern dimension has nearly reached a wavelength of light used in an exposure process. To obtain an even higher accuracy, an electron beam lithography apparatus, which is a charged particle beam apparatus, has been used instead of a photolithography apparatus.
While a pattern formation method (or a photolithography method) using a light source such as an i-beam and an excimer laser is a one-shot exposure method, a pattern formation method using the electron beam lithography apparatus is a direct drawing method (or an electron beam writing method) using a mask pattern. Therefore, there is a disadvantage in the electron beam writing method in which increase in an exposure time (or drawing time) requires a longer time for completing the pattern formation as the number of patterns to be drawn increases. As a result, the higher a degree of integration of a semiconductor integrated circuit becomes, the longer a time required for the pattern formation increases, which raises concerns on reduction of the throughput.
Hereby, to speed up the pattern formation using an electron beam lithography apparatus, a batch graphic irradiation method has been developed, in which electron beams are irradiated in one-shot to combined masks in various shapes, so as to form more complicatedly shaped electronic beams. However, the pattern formation by the batch graphic irradiation method has been resulted in inevitably large-sized apparatus of such an electron beam lithography apparatus and requirement for control in high accuracy of mask alignment. This causes a disadvantage that the apparatus cost increases.
In contradiction to the above, a nanoimprint technology is well known as a technology for forming a fine pattern at low cost. In this nanoimprint technology, the fine pattern can be formed on a resin layer of a transferred object by pressing the stamper having a concavity and convexity (a surface configuration) by using the electron beam lithography technique or the photolithography technique, etc. corresponding to a concavity and convexity of a pattern to be formed against, for example, a transferred object obtained by forming a resin layer on a predetermined substrate. According to such a nanoimprint technology, a fine pattern of a stamper can be transferred to a resin layer.
Further, in the nanoimprint technology, etching on a substrate by a pattern transferred onto a resin layer of the substrate as a resist mask allows a pattern corresponding to the transferred pattern to be formed on the surface of the substrate.
This nanoimprint technology may be applied to the formation of a memory bit in a large volume storage medium, and the pattern formation in a semiconductor integrated circuit.
In the meantime, a structure of pattern transferred onto a resin layer on the substrate by such a nanoimprint technique, is different from a structure of a resist pattern formed by the conventional photolithography technique. That is, the structure of the resist pattern made by the conventional photolithography is formed from only the part to be a mask. On the contrary, the structure of the transferred pattern onto the resin layer by the nanoimprint technique, consists of a convex part formed on the resin layer corresponding to the concave part of the stamper and a concave part formed on the resin layer corresponding to the convex part of the stamper. A thin film layer consisting of the resin remains on the substrate in the concave part formed on the resin layer. Hereinafter, this thin film layer may be referred to as “remaining film part”.
When a pattern of recording bits for a large capacity or a pattern of a semiconductor integrated circuit is created on the substrate, the aforementioned remaining film part and the surface of the substrate covered by the remaining film part are etched using the aforementioned film on the convex part of the resin layer transferred by the nanoimprint technique as an etching mask. According to these methods, a pattern corresponding to the pattern transferred onto the resin layer is formed by etching a part of the substrate corresponding to the concave part of the resin layer.
Note the etching accuracy of the substrate part is affected by the thickness distribution of the remaining film part in the direction along the substrate plate. More specifically, for example, provided etching of 50 nm depth is performed to the substrate in which variation of the thickness of the remaining film part has a differentiation of 50 nm with respect to the maximum thickness and minimum thickness, a part of the substrate having a thin remaining film part may be etched, while apart of the substrate having a thick remaining film part may not be etched completely. Therefore, to maintain the desired processing accuracy of etching, a thickness of a remaining film part formed on a substrate has to be thin and uniform.
Further, in order to form a non-defective microfine structure by using the nanoimprint technology, it is important to control the mold-releasability of the resin layer from the stamper. That is, the mutual adhesion in the interface between the stamper and the resin layer is required to be lower than the mutual adhesion in the interface between the substrate and the resin layer.
According to the above reasons, in order to lower the mutual adhesion in the interface between the stamper and the resin layer, some techniques using a fluorine based mold-releasing agent onto the surface of the stamper is known (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-351693). However, the mold-releasability of the stamper from the resin layer begins gradually deteriorating in proportion as the number of repeatable transfer times onto the resin layer increases. The stamper with deteriorated mold-releasability gives rise to deterioration in the pattern to be transferred on the resin layer. The mold-releasing agent can also be treated again after the stamper has been used repeatedly. However, there is a drawback that the cost of the product obtained from the transferred pattern cannot be lowered enough, from a viewpoint of the number of the repeatable transfer times per one time treatment of the mold-releasing agent with maintaining the predetermined transferring quality.
Another method for enhancing the adhesion between the resin layer and the substrate is also known as a method for preventing a pattern defect from occurring (for example, refer to Japanese Unexamined Patent Application Publications No. 2012-41521 and No. 2009-158729).
In a method disclosed in Japanese Unexamined Patent Application Publication No. 2012-41521, a resinous material for making a resin layer is blended with a silane coupling agent or the like, so as to enhance the (mutual) adhesion between the resin layer and the substrate. Further, in a method disclosed in Japanese Unexamined Patent Application Publication No. 2009-158729, a cohesive layer comprising a silane coupling agent is formed between the substrate and the resin layer, thereby enhancing the cohesive between the resin layer and the substrate.
In the meantime, the releasability of the stamper from the resin layer is attributed to the ratio of the aspect (that is height of the pattern/width of the pattern) and the size of the pattern. Specifically, release of the stamper from the resin layer becomes more difficult, as the ratio of the aspect of the pattern becomes larger and the pattern size becomes smaller. When the aspect ratio of the pattern becomes two or more, the convex parts of the transferred pattern in the resin layer are easy to collapse, and the resinous portion corresponding to the convex part is transferred to the stamper, causing a defect in the transferred pattern in the releasing process.
Due to the recent demand for large sizing and high functionalization for a large scale recording medium and semiconductor integrated circuit, etc., it is anticipated that the pattern on the substrate for these devices becomes smaller, and the ratio of the aspect of the pattern to be prepared becomes larger. Therefore, in order to prepare no defect pattern by applying the nanoimprint technique to the manufacturing of such a large scale recording medium and a semiconductor integrated circuit, etc., a nanoimprint technique (that is, method for forming microfine structure) having the following features is desired. Herein, such a desirable method allows the remaining film part on the substrate to be prepared in a thinner and more uniform manner than the conventional method, and the number of the repeatable transfer times by the stamper per one releasing treatment for the stamper to be greatly increased.
However, as disclosed in Japanese Unexamined Patent Application Publications No. 2012-41521 and No. 2009-158729, the conventional method for improving the mutual adhesion between the resin layer and the substrate has a disadvantage that the adhesion therebetween becomes insufficient when the thickness of the remaining layer becomes thin, which causes the remaining film to be transferred to the stamper.